Many radio-frequency (RF) communication systems transmit information within multiple frequency ranges, or “channels,” of the RF spectrum simultaneously. Because such RF communication systems transmit information by modulating RF carrier signals with the information to be transmitted, devices receiving the modulated RF signals will often need to downconvert such signals so that the original information can be processed as part of a baseband signal. Mixers and/or similar components are used in many communication systems to perform this downconversion.
Mixers typically downconvert RF signals by mixing the RF signal with a tuning signal having a frequency equal to the frequency of the RF carrier signal on which the information was transmitted. As a result, RF receivers often include frequency synthesizers capable of generating tuning signals having frequencies of the same magnitude as the carrier signals which the RF receiver will be receiving. Because many RF communication systems utilize several different carrier frequencies to transmit information, RF receivers in such systems must be able to generate tuning signals of varying frequencies.